The residue bundle supply chain is an additional operation that occurs after the standard cut to length clearfell harvesting of conifers. As per the majority of forest harvesting in Ireland, a harvester and forwarder are used to fell the trees, delimb and crosscut the stem into log lengths, and extract these logs to the roadside. The branches and the tree tops that are left on the forest floor are known as harvesting residues. It is this material that is recovered for use as a fuel.
A residue bundler can be used to gather and compact this material into cylindrical bales. A residue bundling machine is an attachment that is fitted to a forwarder machine. The bunk of the forwarder is removed, and the bundling unit is attached in its place. These bales are often called residue bundles, brash bales, or compact residue logs. These residue bundles are then forwarded out to the forest roadside using a standard forwarder, and transported to the end-user using standard timber trucks. This is an attractive property of the supply chain, the machines used and the links in the chain are already commonly in place in Irish forestry.
When the bundles are delivered to the end-user they are shredded prior to burning in the boiler.
Harvesting could be considered separate from this supply chain as the bundling operations are an addition that occurs after standard harvesting, but it should not be considered so. For instance, a bundler can operated after standard harvesting and extraction of the roundwood products without any prior planning. However, considerable benefits can be made in the bundler productivity and the quality of the fuel from planning for the bundling at the harvesting stage.
Harvesting residues are typically placed under the harvester and forwarder during operations, this is referred to as a brash mat. This brash mat reduces soil damage and helps prevent the machine from becoming stuck. However this also mixes soil with the brash. Planning can incorporate strategies that reduce contamination of the brash by reducing machine passes, and piling residues to one side on suitable sites.
After harvesting, the brash is left on the ground for a period of a few months to allow the material to dry, and the green needles to desiccate an fall off.
The bundling machine drives into the clearfelled area and picks up the loose brash on the ground with its grab. The brash is fed into the bundler, where is is compressed and wrapped with twine in a continuous process. The bundles are cut to a specified length by a built in saw on the bundler.
Forwarding occurs in the same manner are forwarding standard roundwood products. The forwarder does not need to be modified. The forwarder gab is used to load an unload the bundles in the same way as logs. The bundles are stacked at the forest roadside.
Transport is done using standard timber trucks that are commonly seen transporting roundwood throughout Ireland's road network. The cranes on the timber trucks are used to load and unload the bundles in the same way as logs.
When the bundles are delivered to the end user they can be stored until needed. A shredder is used to convert the bundles into hogfuel. Hogfuel is different from chip, in that it is more irregular and produced with blunt tools such as hammers or flails. A shredder is used for the bundles because the bundles comprises of both large round pieces and small branches, which are difficult to chip.